Development of the Skeleton Flashcards
Skull - Parts? Role?
Neurocranium - forms protective case
Viscerocranium - skeleton of the face
Membranous neurocranium - Roles? Development? Bone names? Key characteristics? Fontanelles?
Membranous neurocranium:
- roof and sides of the skull develops from the neural crest cells
- undergo membranous ossification from flat bones
- surrounds the brain and sensory organs (calvaria)
- formed by the parietal, frontal, temporal and occipital bone
- calvaria has no cartilage
- direct ossification of mesenchyme
- fibrous sutures
- allow distortion to pass birth canal
- allow brain growth
- fontanelles: 6, posterior at 3m and anterior at 18
Cartilagenous neurocranium - 2 Parts? Roles? Development? Bone names? Key characteristics? Fontanelles?
Prechondral chondrocranium:
- in front of pituitary gland, derived from neural crest
Chordal chondrocranium:
- posterior to pituitary and arise from paraxial mesoderm
Fuse and ossify by endochondral ossification to form skull base
Cranial base:
- occipital bone, sphenoid, ethmoid, petrous, mastoid part of temporal bones
Viscerocranium - overview? development? pharyngeal arches?
Overview:
- consists of bones of the face
- formed mainly from first 2 pharyngeal arches
- 5 pharyngeal arches (1,2,3,4,6); developing in craniocaudal sequence, 1st pair 22d, 2nd/3rd pair 24d and 2th/6th pair 29d
Cephalogenesis - early chordates?
Early chordates:
- notochord for support
- simple NS
- segmented muscle blocks
- branchial clefts
Cephalogenesis - first vertebrates? skull formation?
Skull formation: Jaw less
- occipital and parachordal cartilages appeared to support notochord in head
- cartilagenous capsules protect sense organs
- branchial arches supported by cartilagenous rods
- cartilage 0 migrates to the head, so 2nd arch cartilage become 1st
Cephalogenesis - first vertebrates (with jaw)?
Skull formation: jaw
- modification of first arch cartilage
- palatopterygoquadrate bar became upper jaw
- Meckel’s cartilage became the lower jaw
- fibrous connection between them was the TMJ
Cephalogenesis - vertebral evolution?
Vertebral evolution:
- brought massive expansion in head
- protecting the brain with additional bont skeletal elements were developed
- from the neuroectoderm, from which neural crest cells migrate and differentiate into ectomesenchyme
Skull development - signalling molecules/genes?
Development:
- Hox gene play key role in craniofacial development
- pharyngeal arches rely on Hox gene expression
- Calvarial growth an cranial suture morphogenesis is regulated by MSX1/2, shh, BMPs, TGF and FGFRs
Newborn skull’s fontanelles - location? fuse dates?
Anterior fontanelle: - between frontal and parietal bones - fuses by age of 2 Posterior fontanelle: - between parietal and occipital bones - fuses by 2-3 months
Newborn skull - comparison to adult skull?
Facial skeleton 1/8 compared to 1/3 adult skull
Newborn skull - development?
Development:
- frontal bone (in 2 halves), suture obliterated in 8th year, can persist as metopic suture
- mastoid and styloid processes absent, facial nerve close to surface at birth (forcep injury)
- palpation of ant. and post. fontanelles, progress of growth of frontal and parietal bones, degree of hydration and level of intracranial Pa
Post-natal period - neonatal period? growth period?
Neonatal period:
- most major bones ossified, but can move relative to another
Growth period:
- sutures permit growth at edges of flat bones
Spheno-occipital synchondrosis - overview?
Overview:
- allows anterior/posterior growth of skull
- closes at 20
Development of the Head - embryonic period? foetal period? post-natal period?
Embryonic period: - pharyngeal arches - facial development - ossification centres Foetal period: - continued ossification Post-natal period: - closure of fontanelles - facial and skull vault growth - sinus expansion - suture fusion - teeth eruption
